1. Field of the Invention
The present invention relates to an encoder in which, as a rotary member is rotated, the states between different combinations of channels switch between a conductive state and a nonconductive state. More particularly, the present invention relates to an encoder in which a pattern of electrode can be easily formed for multiple channels, even if the size of the decoder is decreased.
2. Description of the Related Art
FIG. 7 is an explanatory drawing showing a summary of a construction of a conventional rotary encoder, and FIG. 8 shows wave-form charts (A) and (B) of output from the encoder. For example, an encoder of this kind is disclosed in Japanese Patent No. 2506877.
Conductive sliders 102, 103 and 104 are provided opposite a surface of a disk-shaped substrate 100. On the surface of the substrate 100, a disk-shaped electrode 105, which is formed of a conductive material such as gold, silver and copper, is disposed. The sliders 102, 103 and 104 come into contact with the electrode 105 at three different positions aligned radially with the substrate 100.
In the electrode 105, an inner peripheral region 106 with which the G-channel slider 102 as a common slider comes into contact is formed continuously all round (i.e. 0°-360°) in a rotating direction. An intermediate region 107 with which the H-channel slider 103 comes into contact is formed such that conductive portions 107a and nonconductive portions 107b alternate with each other in the rotating direction. Likewise, an outer peripheral region 108 with which the I-channel slider 104 comes into contact is formed such that conductive portions 108a and nonconductive portions 108b alternate with each other in the rotating direction. The conductive portions 107a and nonconductive portions 107b in the intermediate region 107 are offset by only a slight angle in the rotating direction from the conductive portions 108a and nonconductive portions 108b in the outer peripheral region 108.
The nonconductive portions 107b and 108b are formed by removing part of the electrode 105 to expose a nonconductive surface of the substrate 100.
(A) of FIG. 8 shows a wave form for ON/OFF switching between the H-channel and the G-channel and a waveform for ON/OFF switching between the I-channel and the G-channel when the substrate 100 is rotated in a CW (clockwise) direction relative to the sliders 102, 103 and 104. On the other hand, (B) of FIG. 8 shows a waveform for ON/OFF switching between the H-channel and G-channel and a waveform for ON/OFF switching between the I-channel and G-channel when the substrate 100 is rotated in a CCW (counterclockwise) direction relative to the sliders 102, 103 and 104.
As the substrate 100 is rotated, the state between the H-channel and the G-channel switches between ON and OFF. When the state between the H-channel and the G-channel switches from OFF to ON and back to OFF, the value of count information in a detection circuit is incremented by “1” (in the CW direction) or decremented by “1” (in the CCW direction).
Moreover, since a phase shift Tδ is provided between ON/OFF cycle between the H-channel and the G-channel and ON/OFF cycle between I-channel and the G-channel, the rotating direction of the substrate 100 can be identified. If the state between the H-channel and the G-channel is switched to ON but the state between the I-channel and the G-channel remains unchanged from OFF after the state between the H-channel and the G-channel and the state between the I-channel and the G-channel are both OFF, the rotating direction is CW; if the state between the H-channel and the G-channel remains unchanged from OFF but the state between the I-channel and the G-channel is switched to ON after the state between the H-channel and the G-channel and the state between the I-channel and the G-channel are both OFF, the rotating direction is CCW.
In an encoder of this kind, furthermore, a click mechanism is provided between the substrate 100 and a housing (not shown). For example, an outer peripheral surface of the substrate 100 is repeatedly recessed in the rotating direction and the housing is provided with a plate spring (not shown) for fitting in the recesses. Accordingly, the position of the substrate 100 can be stabilized each time the substrate 100 is rotated by a predetermined angle.
In the invention disclosed in Japanese Patent No. 2506877, the substrate 100 is stabilized when the H-channel slider 103 comes into contact with the nonconductive portion 107b and the I-channel slider 104 comes into contact with the nonconductive portion 108b, i.e., at respective phases CKa, CKb, CKc, etc., as shown in FIG. 8. Japanese Patent No. 2506877 discloses that since the H-channel slider 103 and the I-channel slider 104 are electrically disconnected from each other when the substrate 100 is stabilized, malfunctioning of the circuit can be prevented.
In the conventional encoder shown in FIGS. 7 and 8, the state between the H-channel and the G-channel switches from OFF to ON and back to OFF during rotation for one click angle due to the click mechanism, e.g., during rotation from the stable position CKa to the stable position CKb, and the value of count information in the detection circuit is incremented or decremented by “1” at each rotation for one click operation. That is, one conductive portion 107a and one nonconductive portion 107b for one cycle portion are present within a rotation angle θ for one count up or one count down; one conductive portion 108a and one nonconductive portion 108b for one cycle portion are also present within the rotation angle θ.
Accordingly, if the diameter of the substrate 100 is decreased to reduce the size of the encoder, the area of the substrate 100 within the angle θ is decreased by a substantial amount. This means that one conductive portion 107a and one nonconductive portion 107b for one cycle portion and one conductive portion 108a and one nonconductive portion 108b for one cycle portion need be disposed within this small area. This increases the precision necessary when creating the pattern of the electrode 105, which results in increasing the manufacturing cost and requires an exacting production process such as precision etching or laser processing.
In the conventional encoder, moreover, since the rotating direction is identified with the phase shift Tδ provided between ON/OFF cycle between the H-channel and the G-channel and ON/OFF cycle between I-channel and the G-channel, such a phase shift Tδ need be less than ½ (about ¼) of the ON/OFF cycle. If the substrate 100 is small (for example, the diameter of the encoder is at most about 10 mm), the displacement between the conductive portions 107a and 108a that provides the phase shift Tδ becomes extremely small, so that the rotating direction tends to be erroneously detected if the contact positions of the sliders 103 and 104 (which contact the conductive portions) are slightly displaced.